Enter Zoom Meeting

BG3.22

EDI
Dynamic soil landscapes and climate change

Climate change has already started to affect dynamic feedbacks between plant, soil, and microbial communities and thus strongly influences terrestrial biogeochemical cycling. In this session we address the questions: What is the impact of changing environmental conditions on the plant-soil system, and the resulting effects on soil biogeochemistry? And how do we represent soils in (global) models and upscale experimental data using process-based understanding of the controls on biogeochemical cycles? In this session we seek contributions addressing how biogeochemical cycles in soils vary across gradients in climate, vegetation, and soil properties, and how they may respond to future changes.

We invite contributions from manipulative field experiments, observations in natural-climate gradients, and modelling studies that explore climate change impacts on plant-soil interactions, biogeochemical cycling of C, N, P, microbial diversity and decomposition processes, and deep -soil biogeochemistry. Researchers are encouraged to present their empirical and/or modeling studies addressing soil dynamics along geochemical and climatic gradients. Submissions that adopt novel approaches, e.g. molecular, isotopic, or synthesize outputs from large-scale, field experiments focusing on plant-soil-microbe feedbacks to warming, wetting, drying and thawing are very welcome.

Co-organized by SSS5
Convener: Avni MalhotraECSECS | Co-conveners: Abad Chabbi, Sebastian Doetterl, Allison M. Hoyt, Cornelia Rumpel, Michael W. I. Schmidt
Presentations
| Thu, 26 May, 13:20–18:12 (CEST)
 
Room 3.16/17

Thu, 26 May, 13:20–14:50

Chairpersons: Avni Malhotra, Michael W. I. Schmidt

13:20–13:26
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EGU22-178
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ECS
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On-site presentation
Manon Rumeau et al.

Forests under elevated atmospheric CO2 concentration as a result of climate change are expected to require more available nitrogen (N) to sustain the enhanced CO2 uptake for photosynthesis and C storage. Therefore, it is essential to evaluate how CO2 fumigation of forests will affect availability of N to trees. Main pathways to sustain the high N demand are increasing biological N fixation (BNF), increasing N turn-over and reducing N losses. The purpose of this research is to explore the effects of elevated CO2 on soil N cycling in a temperate forest under the Birmingham Institute of Forest Research (BIFoR) Free Air Carbon Dioxide Enrichment facility. We hypothesize that under CO2 fertilization, trees will allocate more carbon belowground to enhance microbial activity for increasing N mineralization as well as enhancing BNF to meet N demands. We also hypothesize that the subsequent microbial activity will up-regulate N2O and N2 emissions due to denitrification. BNF by free-living organisms is investigated using the 15N assimilation method. Mineralization and N gas production rates is determined using the 15N pool dilution and 15N-Gas flux method at the same time. Early results are showing trends toward an enhancement of N mineralization and microbial N immobilization rates. However, BNF in the forest floor is hardly detectable more likely because of the high N deposition in the area; therefore, it doesn’t appear to be responsive to CO2 fumigation. This research is expected to help us improve our understanding of the changes and magnitude of nutrient availability and gaseous losses under future climates.

How to cite: Rumeau, M., Ullah, S., Mackenzie, R., Carillo, Y., Reay, M., and Sgouridis, F.: Nitrogen cycling in forest soils under elevated CO2: response of a key soil nutrient to climate change, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-178, https://doi.org/10.5194/egusphere-egu22-178, 2022.

13:26–13:32
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EGU22-409
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ECS
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On-site presentation
Noah Sokol et al.

Soil microorganisms are frontline managers of the terrestrial carbon cycle. To better understand and model their effects under a changing climate, it is critical to determine which microbial ecophysiological traits are associated with soil organic matter formation – particularly mineral-associated organic matter (MAOM). Yet major uncertainty surrounds the traits that regulate this process, and how environmental context (e.g. spatial habitat, moisture conditions) shapes the manifestation of these traits. Microbial carbon-use efficiency (CUE) is posited to be a particularly key microbial trait, yet direct evidence for this relationship is sparse, and few other microbial traits have been directly tested as predictors of MAOM formation.

To investigate the relationship between different microbial traits and MAOM, we conducted a 12-week 13C tracer study to track the movement of rhizodeposits and root detritus into microbial communities and SOM pools under moisture replete (15 ± 4.2 %) or droughted (8 ± 2%) conditions. Using a continuous 13CO2-labeling growth chamber system, we grew the annual grass Avena barbata for 12 weeks and measured formation of 13C-MAOM from either 13C-enriched rhizodeposition or decomposing 13C-enriched root detritus. We also measured active microbial community composition (via 13C-quantiative stable isotope probing; qSIP) and a suite of microbial traits that may be important in soil carbon formation, including community-level carbon-use efficiency, growth rate, and turnover (via the 18O-H2O method), extracellular enzyme activity, bulk 13C-extracellular polymeric substances (EPS), and total microbial biomass carbon (13C-MBC).

We found that different microbial traits were associated with MAOM formation in the rhizosphere versus the detritusphere, and their effect was influenced by soil moisture. In the rhizosphere, fast growth and turnover were positively associated with MAOM, as were total 13C-MBC and 13C-EPS production. In contrast, growth rate was negatively associated with MAOM formation in the detritusphere, as were CUE, 13C-MBC, and 13C-EPS. However, extracellular enzyme activity was positively associated with MAOM in the detritusphere. These results, paired with data on the chemical composition of MAOM (via STXM-NEXAFS) suggest that traits associated with fast growth and death rates, as well as high necromass yield, generate microbial-derived MAOM in the rhizosphere, whereas traits associated with resource acquisition generate plant-derived MAOM in the detritusphere. We also present 13C-qSIP data demonstrating that fungal taxa are more active in the detritusphere, whereas certain bacterial phyla (e.g., Firmicutes) are more active in the rhizosphere. Together, our results show that distinct traits, communities, and pathways of MAOM formation predominate in the rhizosphere versus the detritusphere. New research should focus on a broader suite of microbial traits – including but not limited to CUE – to model the role of microbes in MAOM formation in distinct habitats and moisture conditions of the soil.  

How to cite: Sokol, N., Foley, M., Blazewicz, S., Estera-Molina, K., Greenlon, A., Firestone, M., Hungate, B., Slessarev, E., Liquet, J., and Pett-Ridge, J.: Soil habitat and drought shape microbial traits associated with mineral-associated soil carbon formation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-409, https://doi.org/10.5194/egusphere-egu22-409, 2022.

13:32–13:38
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EGU22-500
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ECS
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Virtual presentation
Elena Stoll et al.

Soils are the dominant global source of the important greenhouse gas nitrous oxide (N2O). The anthropogenic input of nitrogen (N) into soil ecosystems increases the rate of soil N cycling, and thus enhances soil N2O emissions. N2O is produced during microbial N transformation processes, mainly via oxic nitrification and anoxic denitrification processes. These predominant pathways depend heavily on soil environmental conditions, such as soil moisture, aeration and substrate availability, which are modulated by weather and climate conditions, atmospheric composition and land use. Consequently, N2O emission rates and pathways are likely to be affected by future global changes in climate and atmospheric composition. However, the combined effects of elevated carbon dioxide (eCO2) and elevated air temperature on both N2O emission rates and pathways are unclear, as the effects can be synergistic, antagonistic or additive, and they can be further influenced by additional interacting disturbances (e.g. summer drought).

Here we test how soil N2O fluxes and emission pathways respond to environmental changes in a multifactorial climate manipulation experiment, combining warming and eCO2, as well as precipitation manipulation to simulate an extreme drought during the growing season in a managed montane grassland. For the first time, we combine in-situ surface N2O flux measurements with online high-time resolution isotopic measurements, soil N2O isotope depth profiles, molecular microbial ecology, and complementary soil and microclimate measurements. Under future global change conditions, we expect increasing N2O emission rates, as well as an increasing importance of denitrification, due to the effect of large emission pulses following rewetting. In addition, we hypothesize that drought effects overrule other environmental change factors. Our results will provide an unprecedented insight into the effects of global changes on soil N dynamics and soil N2O emissions in managed montane grasslands. Furthermore, these findings will help to improve the modelling of N dynamics at the atmosphere-biosphere interface, which will be used to derive soil N2O production and consumption pathways, based on soil N2O isotope measurements, and to upscale the results to examine their potential global relevance.

How to cite: Stoll, E., Diaz-Pines, E., Reinthaler, D., Radolinski, J., Schloter, M., Schulz, S., Duffner, C., Tian, Y., Wanek, W., Pötsch, E., Glatzel, S., Zechmeister-Boltenstern, S., Bahn, M., and Harris, E.: Understanding soil N2O emissions and production pathways in a changing climate by coupling automated chambers with isotope measurements , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-500, https://doi.org/10.5194/egusphere-egu22-500, 2022.

13:38–13:44
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EGU22-1076
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ECS
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On-site presentation
Cyrill Zosso et al.

Soil organic carbon accounts for 2-3 times the amount of carbon (1500-2400 GtC) as compared to the atmosphere, making it an important component of the global carbon cycle. Global warming will also increase soil temperature over the whole soil profiles. As warming experiments to date often focused on topsoils (0-20 cm depth), it is largely unknown how subsoil organic carbon (OC) will be affected by warming, despite the large share of OC stored in subsoils (50% of total soil OC). Furthermore, it remains contentious how temperature sensitive various functional carbon pools are. For example, plant-derived and pyrogenic polymers sometimes have a longer turn-over time as compared to bulk SOC, but could be more sensitive to decomposition under warming.

The whole-soil warming experiment is located in a temperate forest in the Sierra Nevada, CA, US. Soils were warmed by +4°C to 1 m depth with heating rods, maintaining the natural temperature gradient and seasonality. We analyzed plant-derived hydrolysable lipids and the pyrogenic polymers, benzene polycarboxylic acids (BPCA), to better understand the degradation of soil OC and the mentioned polymers.

Our results after 4.5 years of +4°C whole soil warming highlight the vulnerability of even complex plant-derived and pyrogenic polymers in subsoil to warming. Both plant-derived (-27.7±3.3%) and pyrogenic polymers (-37.2±7.9%) were less abundant in subsoils of warmed as compared to control plots, whereas concentrations in topsoils were not affected by warming. These observations underline that in a warming world, previously stable polymeric carbon might be quickly degraded and released to the atmosphere. At the study site, primarily free particulate organic matter was lost, thus the polymeric carbon was potentially part of this unprotected fraction. Taken together, our results underline the importance of studying the effect of soil warming over whole soil profiles. The loss of plant-derived and pyrogenic polymers from warmed subsoils indicates that these compounds are not inherently stable but also prone to degradation in these carbon-limited subsoils with global warming. Our findings contradict the proposed use of plant-derived polymers and pyrogenic carbon for long-term carbon sequestration.

How to cite: Zosso, C., Ofiti, N. O. E., Torn, M. S., Wiesenberg, G. L. B., and Schmidt, M. W. I.: No recalcitrant material in a warming world – Loss of plant-derived and pyrogenic polymers in subsoils after 4.5 years of whole-soil warming, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1076, https://doi.org/10.5194/egusphere-egu22-1076, 2022.

13:44–13:50
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EGU22-1192
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ECS
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Virtual presentation
Francois-Xavier Joly et al.

Strong recent challenges of the long-standing paradigm that macroclimate predominantly controls decomposition questions the accuracy of climate change predictions. With a novel approach combining three experiments at continental scale, using 104 litter types in 194 plots in six major European forests, we show that the confusion around the macroclimate control on decomposition is mostly an experimental artefact. The relative role of decomposition drivers was incorrect when disrupting the natural context of locally-produced litter decomposing locally, with either a focus on litter characteristics neglecting microenvironmental context, or on environmental drivers neglecting local litter characteristics. Our data reaffirm macroclimate and its interaction with litter characteristics as predominant decomposition drivers. Conversely, standard litter types overrated microenvironmental control and failed to predict local decomposition of plot-specific litter. Our findings provide support for a strong macroclimate component in predictive decomposition models and call for cautious interpretation of data from experiments using standard litter types.

How to cite: Joly, F.-X., Scherer-Lorenzen, M., and Hättenschwiler, S.: Cutting the Gordian knot of climate control on decomposition  , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1192, https://doi.org/10.5194/egusphere-egu22-1192, 2022.

13:50–13:56
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EGU22-1320
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Highlight
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Virtual presentation
Paul Hanson et al.

Peatlands represent a dominant source of natural CH4 emissions from the land surface to the atmosphere and the quantitative nature of CH4 emissions for future climatic conditions is a key unknown. The SPRUCE experimental warming by elevated CO2 study located in northern Minnesota has been addressing this question for in situ forested peatland plots since 2016 for five different warming treatments (+0, +2.25, +4.5, +6.75 and +9 °C). Under predominantly wet conditions from 2016 through 2019 (2020 observations were not obtained due to COVID travel restrictions) with minimal reductions in peatland water table levels, CH4 emissions showed an exponential increase across warming treatments with no apparent impact from mid-summer drying conditions nor evidence of a clear elevated CO2 response. The CH4 emissions were less than 1 µmol m-2 s-1 for ambient or low temperature treatments but ranged from 2 to 5 µmol m-2 s-1 under the +6.75 and +9 °C warming treatments.  Moisture and water table levels had minimal impacts on net CH4 flux during this wet period.

The 2021 summer season, however, provided extremely low precipitation and high evapotranspiration that led to reduced average water table depths across the warming treatments to -0.34, -0.45, -0.54, -0.71 and    -0.83 m, respectively. These drought-induced drops in the water table led to aeration of the surface peat layers (acrotelm) and effectively shut off CH4 production in the top layers of the bog. Some evidence for limited net CH4 uptake to the bog during the driest conditions (-0.001 to -0.01µmol m-2 s-1) suggested that CH4 oxidation was playing a role in the reductions of net CH4 emissions. An empirical fitted relationship for net CH4 flux as a function of peat temperatures at -0.2 m and water table depth was developed across all treatments and years. That fitted curve showed that net CH4 emissions were precluded when water table levels dropped below -0.3 m.  This depth corresponds to the peat acrotelm layer containing most of the live root production and activity. The ELM_SPRUCE model was used to fuse the CH4 data to investigate the causes of reduction in CH4 emission. The model was able to reconstruct the dynamics of substrates and CH4 processes under ambient and warming treatments; hydrological feedback was confirmed as warming drives water table drop, which is exacerbated by drought in the summer of 2021.This data-model integration approach suggests the roles of mechanistic models in understanding CH4 cycling in response to warming and drought interactions in future climates.

How to cite: Hanson, P., Phillips, J., Iversen, C., Ricciuto, D., Yuan, F., Zhang, J., and Xu, X.: Drought-induced reductions in net methane emissions from an ombrotrophic peatland are enhanced across a range of experimental warming treatments, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1320, https://doi.org/10.5194/egusphere-egu22-1320, 2022.

13:56–14:02
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EGU22-2066
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ECS
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On-site presentation
Huimin Sun et al.

Global air and soil temperature and nitrogen (N) enrichment are expected to increase in the future, which have the potential to change quantity and quality of soil organic carbon (SOC) pool and alter terrestrial C cycling. However, the underlying mechanism remain unclear especially in the alpine meadow ecosystem on the Tibetan Plateau, which is quite sensitive to global change and is of great importance in regulating future SOC emissions. Using a 9-year two-way factorial experiment involving warming and multilevel N enrichments in the Tibetan Plateau, we showed that both warming and N enrichment promotes soil and microbial C loss. We examined abundance of relative functional genes and found that N enrichment enhanced the ability of microorganisms to degrade labile SOC and reduced the ability to degrade less labile SOC. A long-term laboratory incubation combined with a two-pool model analysis and molecular component examination were conducted to examine potential mechanisms underlying the stabilization variations in different C pools. Diffuse reflectance infrared Fourier transform spectroscopy and biomarker analysis will be used to reveal SOC composition changes and underlying degradation mechanisms. This study highlights the crucial role of soil C stabilization mechanisms in regulating SOC – climate feedback when exposed to warming and chronic atmospheric N enrichment.

How to cite: Sun, H., Schmidt, M., and Nie, M.: Soil organic carbon loss promoted by long-term warming and simulated chronic nitrogen enrichment in the Tibetan Plateau, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2066, https://doi.org/10.5194/egusphere-egu22-2066, 2022.

14:02–14:08
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EGU22-2433
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ECS
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On-site presentation
Binyan Sun et al.

IPCC climate models (RCP8.5) suggest 4°C warming until 2100, which could potentially accelerate soil carbon loss, greenhouse gas release, and thus promote global warming. Despite low carbon concentrations, subsoils (> 30 cm) store more than half of the total global soil carbon stocks. Retaining this is crucial to mitigate soil carbon greenhouse gas release. However, how deep soil carbon will respond to warming and how increased root-derived carbon could contribute to carbon stabilization in subsoils is under-studied and largely unknown. We aim to i) quantify the decomposition rate of root-litter at different depths with a +4°C warming field experiment, ii) assess whether various plant polymers will degrade differently in heated and control plots, iii) identify decomposition products of plant biomass remaining after three years of incubation.

In a field experiment in a temperate forest, 13C labelled root-litter was added at different soil depths (10-14, 45-49, 85-89 cm) in 2016 and retrieved half of the cores in 2017 and the remaining half in 2019. So far, we measured bulk soil carbon concentrations and d13C-composition of individual microbial biomarkers (PLFA).

Results confirm that bulk carbon concentrations and d13C values follow typical depth trends, except for the three horizons containing 13C labelled root-litter incubations. Next, we will quantify above- and below-ground biomarkers (cutin and suberin, respectively) and determine compound-specific 13C-composition in each molecular fraction in heated and control plots. We suspect that the presumably difficult to degrade compounds (cutin, suberin, and lignin polymers) will degrade slower than bulk organic matter over the observation period, and likely faster in heated than control plots. However, early results from warming experiments provide circumstantial evidence that also these compounds might degrade in synchrony with the bulk organic matter.

How to cite: Sun, B., Zosso, C., Wiesenberg, G., Schmidt, M., and Torn, M.: How will belowground plant biomass in deep soil respond to warming in temperate forests?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2433, https://doi.org/10.5194/egusphere-egu22-2433, 2022.

14:08–14:14
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EGU22-3521
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ECS
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On-site presentation
Mathias Mayer et al.

Storms represent a major disturbance factor in forest ecosystems, but the effects of windthrows on soil organic carbon (SOC) stocks are quantitatively poorly known. Here we present a comprehensive analysis of windthrow-induced changes in SOC stocks in Swiss forests by combining field-based measurements and modelling simulations. We measured the SOC stocks of 19 windthrown forests across Switzerland, about 10 and 20 years after they were disturbed by the storms ‘Lothar’ and ‘Vivian’ and compared them to the stocks of adjacent intact forests. We also calibrated the process-based model Yasso07 for additional 77 windthrown forests. Our results show that the effect of windthrow on SOC is strongly related to the size of the initial SOC stocks in the organic layer. In absolute and relative terms, the largest SOC losses occurred in high-elevation forests with thick organic layers, where initial SOC stocks decreased by up to 90% (or 30 t C ha-1). In contrast, SOC stocks of low-elevation forests with thin organic layers were hardly affected. The likely reason for this pattern is the high stocks of easily mineralizable organic matter in thick organic layers of mountain forests, while at low elevations a greater SOC fraction is stabilized by mineral interactions. Modelling simulations further show longer-lasting SOC losses and a slower recovery of SOC stocks after windthrow at high-elevations compared to low-elevations, due to a slower regeneration of mountain forests and associated lower C inputs into soils. We also upscaled the SOC changes after windthrow to the whole forested area of Switzerland and estimated a total SOC loss of ~0.3 Mt C after the storms ‘Lothar’ and ‘Vivian’. Our results provide strong empirical evidence that windthrows can reduce the SOC stocks of forest ecosystems, with mountain forests being hotspots for SOC losses.

How to cite: Mayer, M., Rusch, S., Didion, M., Baltensweiler, A., Walthert, L., Zimmermann, S., and Hagedorn, F.: High soil organic carbon losses in response to forest windthrow , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3521, https://doi.org/10.5194/egusphere-egu22-3521, 2022.

14:14–14:20
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EGU22-3647
Hermann Jungkunst et al.

Earth system model are designed to capture our present knowledge of soil-carbon-climate interactions. However, uncertainties remain high because mechanistic insights are available at fine scales for which we can never achieve unbiased resolution for global modeling. Consequently, the key challenge gaining global or regional overviews of soil carbon-climate feedbacks is to identify the scale that best reflects the underlying soil processes without getting lost in details. According to latest findings, the dominant control of soil carbon persistence varies with climate, which suggests that overarching proxies at a critical mesoscale combine climatic and soil factors and could enable regionally tailored approaches. Here, the Holdridge Life Zone (HLZ) classification proved to be more than a descriptive tool to guide our understanding of soil carbon-climate interaction allowing for linking top-down (from global to local) and bottom-up (from local to global) approaches. In the talk we will present the results for the indiviaul 38 HLZ and present possibilities to add soil internal controls. Regionally tailored solutions can lead to better management of soil carbon. Improving ‘translations’ from the scales relevant for process understanding to the scales of decision-making is key to sustainable soil management and to improve predictions of the fate of our largest terrestrial carbon reservoir during climate change.

How to cite: Jungkunst, H., Brunn, M., Goepel, J., Ott, S., and Horvath, T.: Finding the sweet scale to understand processes and climate control over soil carbon stocks, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3647, https://doi.org/10.5194/egusphere-egu22-3647, 2022.

14:20–14:26
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EGU22-3712
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ECS
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On-site presentation
Thuc Nguyen and Gilboa Arye

Surfactants are used in the soil for many purposes such as for aiding water infiltration into hydrophobic soils or remediating soil contamination. The effectiveness of surfactants in such applications relies greatly on surfactant surface properties - affected by environmental conditions such as temperature. Under the effect of climate change, soil temperature may fluctuate unpredictably, leading to an ambiguation on the appropriate use of surfactants. Therefore, for precise decisions of surfactant application in the soil, it is necessary to evaluate the impact of temperature on surfactant properties. In this study, we chose Rhamnolipid (RLP) -  a biosurfactant that potentially could be used in soils as an alternative for other non-sustainable synthetic surfactants. Our objective was to investigate the surface properties of RLP under the effect of temperature. Previous studies pre-treated RLP with heat and thereafter characterized its surface properties after reaching room temperature. Our study, on the other hand, monitored the dynamic surface tension of RLP at real-time temperature, ranging from 10 to 45 ºC. For a given temperature, the surface tension as a function of time was measured using the pendant drop technique by an optical tensiometer (OCA-22, Data Physics). The diffusion coefficient of RLP to the liquid/air interface and equilibrium surface tension was calculated. In this presentation, both the dynamic and equilibrium surface properties of the RLP mixture (mono and di-rhamnolipid) as a function of temperature will be shown and discussed.  

How to cite: Nguyen, T. and Arye, G.: Dynamic and equilibrium surface tension of Rhamnolipid: Effect of real-time temperature., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3712, https://doi.org/10.5194/egusphere-egu22-3712, 2022.

14:26–14:32
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EGU22-3970
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On-site presentation
Hojeong Kang et al.

Methane (CH4) is over 25 times stronger greenhouse gas than CO2 on a molar basis, and its concentration increases continuously. Its global budget, however, is yet to be constrained, and the greatest uncertainty is associated with natural sources and sinks. Terrestrial ecosystems are known to uptake atmospheric CH4 by a group of microbes known as methanotrophs. Previous studies have noted that the controlling variables for methane oxidation in forest soils are moisture content, temperature and nutrient availability. However, previous estimation on CH4 oxidation in terrestrial soils exhibit great discrepancy between model estimates and field observations. In this study, we measured CH4 uptake rates monthly in temperate pine forests and seasonally in subtropical forests in Korea for 2 years. In addition, soil chemical properties and microbial composition were monitored to reveal the key controlling variable for the uptake rates. Deciduous forests showed the highest CH4 uptake rate followed by mixed forests and the lowest was observed in coniferous forests. Air-filled porosity and the abundance of methanotrophs were correlated with CH4 uptake rate. Our results as well as meta-analysis of 207 measurements from 84 literature showed that soil organic matter (SOM) content significantly correlated with soil CH4 uptake rate at both regional and global scales, indicating that SOM can be a robust controlling factor for CH4 oxidation. We speculate that SOM content affects soil CH4 oxidation via alters air-filled porosity and available carbon source for facultative methanotrophs. The amount of CH4 oxidation in global forests estimated by a model based on SOM content is 22.22 Tg, which far exceeds previous estimation of 17.46 Tg.

How to cite: Kang, H., Lee, J., and Oh, Y.: Soil organic matter as a key controlling variable for methane oxidation in forest soils – microbial analysis and global estimation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3970, https://doi.org/10.5194/egusphere-egu22-3970, 2022.

14:32–14:38
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EGU22-4427
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ECS
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On-site presentation
Steve Kwatcho Kengdo et al.

Climate warming is predicted to affect temperate forests severely, but the response of fine roots, key to plant nutrition, water uptake, soil carbon and nutrient cycling is unclear. Understanding how fine roots will respond to increasing temperature is a prerequisite for predicting the functioning of forests in a warmer climate. We studied the response of fine roots and their ectomycorrhizal (EcM) fungal and root-associated bacterial communities to soil warming by 4 °C in a mixed spruce-beech forest in the Austrian Limestone Alps after 8 and 14 years of soil warming, respectively. Fine root biomass and fine root production were 17% and 128% higher in the warmed plots, respectively, after 14 years. The increase in fine root biomass (13%) was not significant after 8 years of treatment, whereas specific root length, specific root area, and root tip density were significantly higher in warmed plots at both sampling occasions. Soil warming did not affect EcM exploration types and diversity, but changed their community composition, with an increase in the relative abundance of Cenococcum at 0 – 10 cm soil depth, a drought-stress tolerant genus, and an increase in short and long-distance exploration types like Sebacina and Boletus at 10 – 20 cm soil depth. Warming increased the root-associated bacterial diversity, but did not affect their community composition. Soil warming did not affect nutrient concentrations of fine roots, though we found indications of limited soil phosphorus (P) and potassium (K) availability. Our findings suggest that, in the studied ecosystem, global warming could persistently increase soil carbon inputs due to accelerated fine root growth and turnover, and could simultaneously alter fine root morphology and EcM fungal community composition towards improved nutrient foraging.

How to cite: Kwatcho Kengdo, S., Peršoh, D., Schindlbacher, A., Heinzle, J., Tian, Y., Wanek, W., and Borken, W.: Long-term soil warming alters fine root dynamics and morphology, and their ectomycorrhizal fungal community in a temperate forest soil, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4427, https://doi.org/10.5194/egusphere-egu22-4427, 2022.

Thu, 26 May, 15:10–16:40

Chairpersons: Sebastian Doetterl, Abad Chabbi, Cornelia Rumpel

15:10–15:16
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EGU22-4506
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ECS
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On-site presentation
Dario Püntener et al.

Carbon cycling in alpine soils is prone to changes with temperature increase, for instance because of reduced frost periods (Zierl & Bugmann, 2007). Afforestation throughout the last decades and in future with warming climate and land-use change will influence carbon dynamics. To investigate the climate-driven response of carbon cycling in alpine soils, we conducted a jar incubation experiment under controlled conditions using 13C-labelled plant material and traced the decomposition of the organic material under different increasing temperature regimes.

Approximately 20 kg of soil samples were collected from the uppermost 10 cm of a 130-year old tree stand and a pasture site from a sub-alpine afforestation sequence in Jaun, Switzerland. The samples were sieved to 2 mm, roots and stones were removed. 50 g of the soil material was incubated in 2 l glass jars.

To investigate the degradation of the organic material, dried and cut shoots of 13C labelled plant material (Lolium perenne L.) were added to the soil samples. Additionally, samples without added plant material were incubated as a control group. The incubation was conducted at three different temperature regimes: 12.5°C (average growing season temperature, weather station by WSL-SLF, 2021), 16.5°C (+ 4°C) and 20.5°C (+ 8°C). Destructive sampling was conducted after 0, 2, 4, 8, and 26 weeks. NaOH traps were exchanged every 3-4 days in the beginning and every 3 weeks during later stages of the experiment to trace the respiration of CO2 and the 13C label.

The measured basal respiration shows a temperature dependence. The values are highest at 20.5°C and subsequently decreased to 16.5°C and 12.5°C with the lowest basal respiration. Surprisingly, the basal respiration of the forest soil is always higher than that of the pasture soil of the same incubation temperature. This partially contradicts previous findings (Nazaries et al., 2015) and might be related to the more resilient microbial community in the forest compared to the pasture soil.

Litter-induced respiration increased sharply after litter application and then decreased again. The pasture soil shows higher cumulative respiration for each temperature compared to the forest soil incubated at the respective temperature. After the highest litter-induced respiration of the pasture soil at 20.5°C at the beginning, this is surpassed by that of the pasture soil with 16.5°C from about 40 days after the beginning of incubation. This could indicate a temperature optimum of the current soil microbial community closer to 16.5°C rather than to 20.5°C. These initial results indicate a different sensitivity of the soil microbial community and consequently also carbon cycling in alpine soils to future rising temperature depending on vegetation cover.

Nazaries, L., Tottey, W., Robinson, L., Khachane, A., Al-Soud, W. A., Sørenson, S., & Singh, B. K. (2015). Shifts in the microbial community structure explain the response of soil respiration to land-use change but not to climate warming. Soil Biology and Biochemistry, 89, 123–134.

WSL-SLF (2021), IMIS Weather Station Fochsen-Jaun, WSL, Davos/Switzerland.

Zierl, B., & Bugmann, H. (2007). Sensitivity of carbon cycling in the European Alps to changes of climate and land cover. Climatic Change, 85(1–2), 195–212.

How to cite: Püntener, D., Speckert, T. C., Thomas, C. L., and Wiesenberg, G. L. B.: Non-uniform Soil Respiration of Soils from an Afforestation Sequence in a Laboratory Incubation Experiment, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4506, https://doi.org/10.5194/egusphere-egu22-4506, 2022.

15:16–15:22
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EGU22-4539
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ECS
Jakob Heinzle et al.

Trees invest up to one third of the carbon (C) fixed by photosynthesis into belowground allocation, including fine root exudation into the rhizosphere. Rising soil temperatures in a warmer world could modify the allocation of labile C below ground, thereby affecting biogeochemical cycling in forest soils. Up to date our understanding of how fine root exudation of labile carbon compounds responds to warming is yet emerging and in-situ analyses under warming conditions are scarce, especially in mature forests. Using a C-free cuvette incubation method, we investigated in situ rates of root exudation from fine roots in a mature spruce forest across three seasons after 14 and 15 years of warming in the Achenkirch soil warming (+4°C) experiment. In addition, we run a complementary short-term experiment on root exudation, during which we increased soil temperatures on warmed plots stepwise up to a difference of 12°C between treatments within a few days. We found no effect of long-term soil warming on in situ root exudation rates (n = 120 roots sampled). Mean exudation rates per biomass were 16.23 ± 4.03 and 17.94 ± 2.94 µg g-1 h-1 on control and warmed plots respectively, with highest rates found in the late growing season in both treatments. Exudation rates were positively related to the specific root length and were negatively related to soil moisture, but unrelated to soil inorganic N availability and in situ soil temperature. However, the short-term temperature manipulation resulted in an exponential increase of estimated root exudation rates with soil temperature. Our results therefore indicate that fine root exudation from mature trees in the studied ecosystem is inherently controlled by soil temperature, but an interplay with other parameters such as nutrient availability, root morphology and/or soil moisture are the dominant controlling mechanisms across the seasons in the long run. Our observations further indicate that the long-term soil warming by 4°C caused only a subtle increase in root exudation per fine root surface area or per fine root biomass.

How to cite: Heinzle, J., Liu, X., Tian, Y., Kwatcho-Kengdo, S., Borken, W., Inselsbacher, E., Wanek, W., and Schindlbacher, A.: Effects of soil warming on in situ fine root exudation rates in a temperate forest soil, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4539, https://doi.org/10.5194/egusphere-egu22-4539, 2022.

15:22–15:28
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EGU22-4938
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On-site presentation
Wolfgang Wanek et al.

The capacity of forest soils and trees to sequester C is closely linked to soil nitrogen (N) bioavailability, a major control of microbial and plant growth and functioning. Recent meta-analyses indicated that both, soil organic C and N cycling, intensify with climate/soil warming, though little studies investigated this in long-term (decadal) warming experiments. Changes in N cycling processes have been addressed by measuring total and labile N pools, net and gross N process rates, and changes in extracellular enzyme activities. An alternative approach, integrating over longer time intervals, is to study the natural 15N abundances of different soil and plant N pools. In this study we quantified the natural 15N abundances (d15N values) of coarse and fine litter, fine roots, soil organic N, extractable organic N, microbial biomass N, ammonium and nitrate at the long-term soil warming experimental site in Achenkirch (Tyrol, Austria). This site is one of the few climate manipulation experiments in forests operating for more than 14 years and has provided unique insights into the effects of global warming on forest ecosystem processes. We analyzed ecosystem compartments across three seasons (May, August, October 2019), to investigate the consistency of warming effects on soil N cycle processes. Moreover, we developed an isotope fractionation model to decipher the isotope fractionations of the studied soil N processes and the fractions transformed by them, i.e. for depolymerization, microbial uptake, N mineralization, nitrification and soil N losses. Overall, the consistent increase in fine root δ15N in warmed soils indicated a general opening of the soil N cycle (greater N losses), which was mirrored in increased ammonium d15N values, the latter implying increased fractions of ammonium being oxidized to nitrate. Higher fractions of ammonium being nitrified makes labile N more amenable to N losses, either by leaching of nitrate or by denitrification losses. Since nitrification and denitrification exhibit strong isotope fractionation effects against 15N, the lost N is concomitantly 15N depleted, while residual substrates remaining in the ecosystem become 15N enriched, thereby explaining the 15N enrichment with increasing N cycling and N loss rates in warmed soils. 

How to cite: Wanek, W., Bachmann, M., Inselsbacher, E., Heinzle, J., Tian, Y., Kwatcho-Kengdo, S., Shi, C., Borken, W., and Schindlbacher, A.: Effects of long-term soil warming on soil organic and inorganic nitrogen cycling in a temperate forest soil as assessed by measurements of natural 15N abundances of soil N pools, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4938, https://doi.org/10.5194/egusphere-egu22-4938, 2022.

15:28–15:34
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EGU22-5545
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On-site presentation
Michael W. I. Schmidt and Avni Malhotra and the "Global Deep Soil 2100" network

"Global Deep Soil 2100" is a network for whole-ecosystem warming experiments. The aim of DeepSoil 2100 is to bring together researchers working on long-term soil experiments particularly focused on deep soil horizons (at least 1 m). The year '2100' was chosen because IPCC scenarios run until 2100. We welcome whole ecosystem warming manipulations, with or without other manipulations such as water and carbon dioxide concentrations, and studying responses of plants, soil biogeochemistry, ecology, etc.

Globally, there are less than a dozen whole-ecosystem warming experiments but not all researchers know about each other. To introduce experiments and involved scientists, we started video meetings at the end of 2020. This effort brought together experimentalists, modelers and data users into this "whole-ecosystem warming network", to share practical experience on field experiments, data reporting, discuss observations and results and explore synergies regarding tools, knowledge, and data sharing and interpretation. We hope that this network will serve as a basis for future data syntheses and coordinated sampling efforts.

View previous meeting recordings here:  https://tube.switch.ch/channels/ed725365
 
Further details and contact can be found on the webpage of the "International Soil Carbon Network"
https://iscn.fluxdata.org/network/partner-networks/deepsoil2100/

 

How to cite: Schmidt, M. W. I. and Malhotra, A. and the "Global Deep Soil 2100" network: Introducing the "Global Deep Soil 2100" network, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5545, https://doi.org/10.5194/egusphere-egu22-5545, 2022.

15:34–15:40
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EGU22-5581
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ECS
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Highlight
Do soil microbes adapt to warming?
(withdrawn)
Gabriel Moinet et al.
15:40–15:46
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EGU22-5625
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ECS
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On-site presentation

Climate change is expected to alter plant growth and traits, and in turn alter the quantity and quality of plant-derived carbon inputs to soils. Even though root-derived carbon inputs are more likely to be stabilized as soil organic matter (SOM) than aboveground inputs, our models of how climate change influences plant traits and SOM often focus on aboveground plant dynamics. This is in part because our knowledge of root trait linkages to SOM is limited. Recent efforts synthesizing root trait and soil data make it possible to harmonize these data towards an improved representation of roots in terrestrial biosphere models but a conceptual framework to do this is missing. To this end, we review processes that bridge root traits to SOM formation and stabilization and suggest future model improvements. We estimated that 80% of total global soil carbon is in the rooting zone. We then determined that root traits relevant for SOM can be broadly divided into those pertaining to either living or dead roots, within which, the amount, characteristics, and lifespan of living roots, and the decomposability of dead roots and root fragments are particularly important for SOM. Model recommendations included improved allocation regimes, representation of root interactions with microbes and minerals, and incorporation of root-trait variation across the heterogeneous soil matrix. Our review provides a framework necessary for data syntheses and modelling of root trait-SOM linkages to understand future changes in SOM driven by changing plant inputs in a warmer and elevated atmospheric CO2 world. 

How to cite: Malhotra, A. and the Root trait-soil carbon working group: Linking root traits to soil carbon: model and data gaps, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5625, https://doi.org/10.5194/egusphere-egu22-5625, 2022.

15:46–15:52
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EGU22-5636
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ECS
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On-site presentation
Keli Li et al.

One of the consequences of climate change is the frequency of extreme weather incidences, such as extreme drought or heavy rainfall increase. At the same time, climate warming enables certain plant species to expand to higher latitudes. The question is how the frequency of extreme drought or heavy rainfall affects plant-soil interactions of range-shifting plants in the new habitat compared to native residents. We conducted an outdoor mesocosm experiment to study how an extreme drought influenced biomass production of range-shifting and co-occurring congenetic native plant communities in the next year by plant-soil feedback. We found that in soils with a history of extreme drought range-shifting plants produced more shoot biomass. To explore mechanisms in more detail, we set up a greenhouse experiment to condition soils under extreme drought and heavy rainfall. Then, we tested plant-soil feedbacks using Centaurea jacea as native and Centaurea stoebe as range expander. Our results showed during soil conditioning under extreme drought the shoot biomass was decreased, and under extreme wet conditions was increased. This applied to both range expander and native species. At the same time, soil N, P, and K and soil microbial communities had changed in a different manner. Consequently, these soil biotic and abiotic changes might be the main drivers of negative, neutral, positive plant-soil feedbacks of range expanders and natives under extreme weather events, with an impact on plant quality changes and plant-associated herbivore responses. Thus, we show that climate change may influence both plant biomass and aboveground herbivory through altering plant-soil biota interactions.

How to cite: Li, K., (G.F.) Veen, C., A. Harvey, J., and H. van der Putten, W.: Extreme drought or heavy rainfall drives plant-soil feedbacks of range-shifting and congeneric native plant species, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5636, https://doi.org/10.5194/egusphere-egu22-5636, 2022.

15:52–15:58
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EGU22-6123
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ECS
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On-site presentation
Julia Miloczki et al.

Climate models predict an increase in the average temperature, an increase in heat and drought periods in summer and heavier rainfall events for Austria (APCC, 2014; IPCC, 2021). Eventually, advancing droughts can lead to substantial yield losses, which will be more pronounced on soils with low water storage capacity (Eitzinger et al., 2013). Especially in dry regions like the Marchfeld (east of Vienna), Austria’s most productive region for grain and vegetables, this may have severe consequences for food security.

In our study, we investigated the combined effects of different soil types and altered precipitation on the soil-plant-nexus in a lysimeter facility from 2017-2019. This facility consists of 18 gravitation lysimeters representing the three main soil types of the Marchfeld, namely calcaric Phaeozem (Ps), calcic Chernozem (Ch) and gleyic Phaeozem (Pg). Half of the lysimeters were irrigated according to current precipitation patterns and half according to the precipitation pattern predicted for the period 2071-2100 in the Marchfeld region, simulating drought periods and heavy rain events. Spring wheat, spring barley and winter wheat were cultivated in all lysimeters in 2017, 2018 and 2019, respectively. Mustard was cultivated as a cover crop after spring wheat and incorporated as mulch. The following spring barley had substantially higher yields than spring wheat. This might be due to the improved water infiltration and organic matter input provided by the cover crop (Kirchman, 2011) and/or the larger crop damage by animals in 2017. 

Drought events resulted in an average decline of grain yield by 66% (p<0.05) in spring wheat, 40% (p=0.13) in spring barley and 39% (p<0.05) in winter wheat. In all soil types, the yield of winter wheat was higher than of the other crops, which could indicate its ability to make better use of water resources than the spring crops. This underlines the importance of optimizing sowing dates as an adaptation strategy to climate change. The increase of the δ13C value, an indicator for the stomata conductance, in the “predicted” scenario confirmed that drought stress was limiting plant growth.  δ13C values were also higher in the Phaeozem than in the Chernozem, with the first having a lower soil water holding capacity.

In contrast to biomass, nitrogen content of grain did not change between current and predicted precipitation patterns, indicating no impairment of grain quality. Furthermore, the nitrogen use efficiency tended to be higher in the current scenario than in the predicted scenario and was highest for winter wheat. Overall, plant biomass, plant nitrogen content and plant δ15N values were differently affected by soil type, however as there were no significant interaction effects with precipitation, plants responded identically to the precipitation pattern on all soil types, i.e. significant decline in crop production under drought stress.

Our results exemplify the pressing need to develop and implement adaptation strategies in agriculture, taking into consideration local pedoclimatic characteristics. Introducing more resilient crop species, diversifying the crop rotation and increasing the system’s water use efficiency are promising measures that should be investigated further.

How to cite: Miloczki, J., Prommer, J., Wawra, A., Berthold, H., Hösch, J., Formayer, H., Kisielinska, W., Spiridon, A., Hood-Nowotny, R., Spiegel, H., Baumgarten, A., and Watzinger, A.: Climate change induced drought inhibits plant growth in agricultural systems – A lysimeter study, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6123, https://doi.org/10.5194/egusphere-egu22-6123, 2022.

15:58–16:04
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EGU22-6813
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ECS
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Highlight
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On-site presentation
Katerina Georgiou et al.

Soils contain the largest actively-cycling terrestrial carbon pool, which is itself composed of chemically heterogeneous and measurable pools that vary in their persistence. Fundamental uncertainties in terrestrial carbon-climate feedbacks still depend on the timing, sign, and magnitude of the response of soil carbon, and its underlying pools, to environmental change. However, model comparisons typically focus on benchmarking only bulk soil carbon stocks and climatological temperature sensitivities. Underlying microbial and mineral-associated pools, and their response to global change, have received increasing attention among empirical studies, yet data limitations still hinder benchmarking of these pools and processes in models at ecosystem- to global-scales. Here we examined the distribution of carbon within particulate and mineral-associated fractions across an ensemble of global soil biogeochemical models, and compared model estimates to a global database of soil fractions. We found that, while bulk soil carbon stocks were seemingly comparable in magnitude and geographic distribution across the models and observations, the spread in underlying pools was much more pronounced. Indeed, the ensemble of models varied nearly 6-fold in the proportion of carbon in mineral-associated fractions, and the majority of models greatly underestimated mineral-associated carbon stocks compared to the observations. Latitudinal differences between the models resulted in divergent pool-specific climatological temperature sensitivities, with implications on projections to global change scenarios. Our study elucidates key structural and theoretical differences between models that drive divergent soil carbon projections, and clearly highlights the need to benchmark underlying carbon pools, in addition to bulk soil carbon stocks.

How to cite: Georgiou, K., Wieder, W. R., Abramoff, R. Z., Koven, C. D., Riley, W. J., Ahlström, A., Bouskill, N. J., Hartman, M., Pellegrini, A., Pierson, D., Sulman, B., Slessarev, E., Zhu, Q., Pett-Ridge, J., and Jackson, R. B.: Global distribution and climatological temperature sensitivity of soil organic matter fractions differ between observations and models , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6813, https://doi.org/10.5194/egusphere-egu22-6813, 2022.

16:04–16:10
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EGU22-7946
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ECS
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Virtual presentation
Meret Aeppli et al.

Mountain floodplains are characterized by spatiotemporal variations in soil redox conditions that arise due to dynamic hydrological and resulting biogeochemical states. Under oxygen-depleted conditions, solid phase Fe(III) can serve as terminal electron acceptor (TEA) in anaerobic microbial respiration. It remains unclear, however, to what degree the redox properties of Fe(III) phases limit rates of anaerobic respiration and hence organic matter degradation. Here, we assess such limitations in iron-rich soils collected across a gradient in native redox states from the Slate River floodplain (Colorado, U.S.A.). We incubated soils under anoxic conditions and quantified electron transfer to TEAs, TEA reactivity toward electrochemical reduction, and CO2 production. Fe(III) reduction occurred together with CO2 production in native oxic soils; no Fe(II) nor CO2 production was observed in native anoxic soils. Initial CO2 production rates increased as the reactivity of TEAs toward electrochemical reduction increased across all soil depths and, thus, native soil redox states. The low redox reactivity of TEAs was likely caused by higher acid-extractable Fe(II) concentrations rather than higher crystallinity of Fe(IIII) mineral phases based on analysis of Fe(III) mineral identity and crystallinity using Mössbauer spectroscopy. Our findings indicate that the low redox reactivity of TEAs limited microbial respiration rates in our incubation experiments. This work advances our understanding of controls on anaerobic microbial respiration and can help anticipate organic matter degradation under future hydrological conditions.

How to cite: Aeppli, M., Thompson, A., Dewey, C., and Fendorf, S.: Redox properties of particulate electron acceptors affect anaerobic microbial respiration under oxygen-limited conditions in floodplain soils, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7946, https://doi.org/10.5194/egusphere-egu22-7946, 2022.

16:10–16:16
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EGU22-8723
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ECS
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On-site presentation
Arthur Broadbent et al.

Climate change is disproportionately impacting mountain ecosystems, leading to large reductions in winter snow cover, earlier spring snowmelt and widespread shrub expansion into alpine grasslands. Yet, the combined effects of shrub expansion and changing snow conditions on abiotic and biotic soil properties remains poorly understood. We used complementary field experiments to show that reduced snow cover and earlier snowmelt have effects on soil microbial communities and functioning that persist into summer. However, ericaceous shrub expansion modulates a number of these impacts and has stronger belowground effects than changing snow conditions. Ericaceous shrub expansion did not alter snow depth or snowmelt timing, but did increase the abundance of ericoid mycorrhizal fungi and oligotrophic bacteria, which was linked to decreased soil respiration and nitrogen availability. Moreover, by combining molecular sequencing, enzyme assays, greenhouse gas flux measurements, soil biogeochemical analyses, and 15N labelling, we show that reduced winter snow cover and shrub expansion alter the seasonal dynamics of plant growth (i.e., net ecosystem exchange and plant N-uptake), with important consequences for the seasonal dynamics of soil microbial communities, their functioning, and alpine biogeochemical cycles. In conclusion, our findings suggest that changing winter snow conditions have cross-seasonal impacts on biotic and abiotic soil properties, but shifts in vegetation can modulate belowground effects of future alpine climate change.

How to cite: Broadbent, A., Bahn, M., Pritchard, W., Newbold, L., Goodall, T., Guinta, A., Snell, H., Cordero, I., Michas, A., Grant, H., Soto, D., Kaufmann, R., Schloter, M., Griffiths, R., and Bardgett, R.: Changing snow conditions and shrub expansion alter above- and belowground seasonal dynamics in alpine grasslands, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8723, https://doi.org/10.5194/egusphere-egu22-8723, 2022.

16:16–16:22
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EGU22-8949
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ECS
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Highlight
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On-site presentation
Feng Tao and Yiqi Luo

Soil carbon cycle is a large yet poorly understood component of the global carbon cycle under climate change. The transient behaviour of the soil carbon cycle is fully determined by four elements, which are carbon input, residence time,carbon pool size (or state), and the net carbon flux. Many of the past studies focused on one subset of the four elements to quantify soil carbon sequestration under climate change, often leading to contradictory conclusions. Here we assimilated data of respired soil 14C, soil 14C profile, and soil organic carbon (SOC) profile from Harvard Forest (i.e., a mid-latitude hardwood forest) into a vertically resolved process model (i.e., Community Land Model version 5, CLM5) together with estimated carbon input to fully constrain soil carbon dynamics during 1900 to 2010. Our results suggested litter pools instead of the mineral soil pools contributed to the majority of the carbon sequestration in history. Different sources of constraints effectively informed parameters of their corresponding elements in the soil system. Yet, single data constraints only provided part of the features of soil carbon cycle and cannot lead to a comprehensive interpretation of its historical dynamics. Using 14C data alone as the constraints resulted in overestimated soil carbon residence time and more sensitive responses of soil carbon sequestration to changing climate. In the future, multi-source data constraints from different global databases are essential in understanding soil carbon dynamics and accurately quantifying soil sequestration in response to the changing climate across the globe.

How to cite: Tao, F. and Luo, Y.: Quantifying soil carbon sequestration by multi-source constraints, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8949, https://doi.org/10.5194/egusphere-egu22-8949, 2022.

Thu, 26 May, 17:00–18:30

Chairpersons: Abad Chabbi, Avni Malhotra, Michael W. I. Schmidt

17:00–17:06
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EGU22-10533
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ECS
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Virtual presentation
Joana Serôdio et al.

Drylands are unique and diverse ecosystems that occupy more than 40% of the terrestrial surface. These areas are inhabited by more than 35% of the world population. In the case of Portugal, drylands represent 37% of its territory. In many areas worldwide, climate change (CCh) is increasing the aridity leading to an expansion of drylands. However, the joint effects of different CCh drivers on the features, functions, and services of drylands remain largely unknown. Further, there is large uncertainty on how CCh-driven alterations in biotic and abiotic soil attributes will feedback CCh through greenhouse gas (GHG) fluxes.

This study aims to assess (1) the soil-atmosphere GHG exchange and soil nutrients availability and (2) their response to different CCh scenarios along an aridity gradient made up of 8 humid, arid, and semiarid-natural parks in Portugal. In winter 2019, we installed open top chambers and rainfall shelters (both separately and combined) in 24 plots to simulate the forecasted increase in temperatures (~3 °C) and reduction in precipitation (~35%), respectively. Since then, seasonal field campaigns to collect gas and soil samples as well as to measure in situ nutrients availability have been performed.

Our first data show that soil organic matter and nutrients (N and P) availability decrease along the aridity gradient whereas methanogenesis seems to be constrained along the gradient and there is not a clear response from other GHG to the aridity gradient. Soil respiration was mainly driven by the seasonal variability of soil moisture and temperature. Finally, the different CCh scenarios had their biggest effect on variables with faster turnover and the response of GHG fluxes to different CCh scenarios varied among sites, which highlights the importance of considering other site-dependent ecosystem features when trying to assess the effects of climate change on GHG fluxes.

How to cite: Serôdio, J., Férnandez-Alonso, M. J., Fangueiro, D., Freitas, H., Durán, J., and Rodríguez, A.: Greenhouse gas fluxes and nutrients availability in Portuguese drylands and their sensitivity to climate change, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10533, https://doi.org/10.5194/egusphere-egu22-10533, 2022.

17:06–17:12
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EGU22-10985
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ECS
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On-site presentation
Elin Ristorp Aas et al.

Complex biogeochemical processes involving vegetation, microbial communities, symbiotic relationships and nutrient cycling determines the rates at which carbon is transferred between the atmosphere and the soils, and eventually the terrestrial carbon storage. Because of these complexities, there are still large uncertainties connected to the representation of the terrestrial carbon cycling in Earth System Models.

An emerging approach to deal with these problems is to explicitly represent microbial pools as well as physically and chemically protected soil organic matter in the model. Based on this, we have developed a soil decomposition process model designed to capture and quantify relationships between soil microorganisms and their environment, focusing on high latitude systems. Our aim with this approach is dual: 1) Testing hypotheses in the model before designing field experiments will help to set up experiments that benefits both understanding of the ecology and improving the model and, 2) Incorporating such a model into an ESM will make it possible to validate the model with observations, and to identify possible climate feedbacks related to the soil dynamics.

The model includes the decomposer activity of saprotrophic fungal and bacterial communities and the symbiotic relationship between mycorrhizal fungi and vegetation. We include separate carbon and nitrogen reservoirs for these microbes, as well as for plant litter and soil organic matter. The transfer of C and N between the reservoirs is based on rate equations using various parameterizations found in literature, and is also transported vertically following a diffusion equation.

The model is forced with litter input and climatic variables from the Community Land Model (CLM5). For calibration and validation we use subsets from a large dataset containing soil profile data for ~1000 forested sites in Norway (Strand et al. 2016). Since the sites are distributed over a large area, they cover climatic gradients in both temperature and precipitation.

Comparisons of C and N content between simulations from the new decomposition model, the standard CLM5 and the observations will be presented, as well as sensitivity tests of different parameter choices and impacts of changes in climate forcing.

How to cite: Ristorp Aas, E., Koren Berntsen, T., Eiler, A., and de Wit, H.: Representing microbial activity in a soil decomposition model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10985, https://doi.org/10.5194/egusphere-egu22-10985, 2022.

17:12–17:18
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EGU22-11445
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Virtual presentation
Anastasia Makhnykina et al.

The current climate changes exert influence on these ecosystems by changing water supply, temperature regime, plant growing activity and others. Nowadays studies predicted the important role of the northern bogs and peatlands as an additional source of atmospheric CO2. The research area was located in the Krasnoyarsk region, Russia (60° 48’ N, 89° 22’ E) close to the International research station – ZOTTO (http://www.zottoproject.org).  In our study we estimated how microrelief and microclimatic conditions can control the CO2 emission from the bog and forested areas. We compared also the waterlogged bog conditions and forest ecosystem to find out the main drivers of soil emission dynamics during the summer season. The rate of CO2 emission varies widely within the bog area depending on the microrelief of the area: hollow site – 0.74 ±0.03, ridge site – 1.69 ±0.08 kg CO2 m-2. Comparative analysis with the forest area showed that the upland parts of the bog area are not inferior to the forest area in terms of the CO2 emission rate. Moisture conditions determined the CO2 efflux for the hollow site (r=0.49, p<0.05) and forested area (r=0.39, p<0.05). The temperature impact is observed for all sites and it is significant throughout the season. Thus, within a single bog area micrometeorological characteristics of the underline surface during the season significantly control the CO2 emission rates.

 

The research was funded by RFBR, Krasnoyarsk Territory and Krasnoyarsk Regional Fund of Science, project number 20-44-243003.

How to cite: Makhnykina, A., Polosukhina, D., and Prokushkin, A.: Soil CO2 emission in the boreal zone of Central Siberia: raised bog and lichen pine forest ecosystems, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11445, https://doi.org/10.5194/egusphere-egu22-11445, 2022.

17:18–17:24
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EGU22-11645
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ECS
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On-site presentation
Linsey M. Avila et al.

The impact of rising global temperatures on carbon cycling in some of our most sensitive ecosystems, such as the Arctic, is critical yet challenging to quantify because short- and long-term effects of warming may be different. The observed short-term temperature response of soil organic carbon (SOC) decomposition may be altered in the long-term due to changes in substrate availability and possible acclimation of soil communities. 

Testing how the temperature response of soil decomposition changes over time with warming under open-air, field-scale conditions presents another obstacle for researchers, as warming experiments at different temperatures and over long measurement periods are expensive and rare. Fortunately, the ForHot grassland site in Iceland has provided us with a unique opportunity to explore soil warming effects by measuring along a naturally occurring geothermal gradient that resulted from an earthquake back in 2008.

As part of the FutureArctic project at the ForHot site, we collected five replicate soil cores to a soil depth of 5 cm (100cm3 per sample), from fourteen plots along the geothermal gradient spanning a soil warming gradient from 0°C to +80°C. The samples were incubated in the lab at 5, 15, 25, and 35°C, and flux rates of CO2 and CH4 were measured using a LGR-ICOS M-GGA-918 to produce observational Q10 temperature response relationships. 

Temperature response rates and curvature appeared to be driven primarily by substrate availability. Samples containing the greatest totals of carbon and nutrients produced the highest rates of CO2 emission and CH4 consumption at all temperatures. This likely being an effect of the 13 years of warming where organic content and spatial proximity to the hotspot are inversely correlated. From this, we can then present an analysis of the potential linearity or nonlinearity that temperature responses can have over a rather extensive temperature gradient and how these responses can change over time.

Samples collected from the hotspot, where previous in-situ chamber measurements have shown the highest emissions of CO2 and CH4, had significantly lower CO2 emissions and essentially no flux of CH4 during the laboratory incubations. This suggests a significant contribution of geogenic sourcing to in situ measurements. We present an analysis of the potential use for laboratory incubations at different temperatures to infer geogenic/biogenic flux contributions for in situ measurements where geogenic CO2 and CH4 emissions are present. This will allow us to construct a corrected biogenic carbon budget of the ForHot ecosystem and improve our fundamental understanding of the long-term effects that rising temperatures have on the carbon cycle in subarctic ecosystems. 

How to cite: Avila, L. M., Sigurdsson, B. D., Riis Christiansen, J., and Steenberg Larsen, K.: Disentangling long-term and short-term temperature response of carbon fluxes in a subarctic grassland ecosystem exposed to long-term, geothermal warming , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11645, https://doi.org/10.5194/egusphere-egu22-11645, 2022.

17:24–17:30
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EGU22-12663
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ECS
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On-site presentation
Biplabi Bhattarai et al.

Climate predictions for arctic and subarctic regions show a higher rise in surface temperature than the global mean, which will subsequently raise the soil temperature (Ts) in those regions. We investigated the effects of soil warming duration (medium-term (11-yr) vs. long-term (>60-yr) warmed grassland) and magnitude from +0.2 to +6.2 °C on total belowground plant biomass (BPB) as well as in two functional groups: short-living fine-roots and long-living rhizomes in topsoil (0-10cm) and subsoil (10-30cm). We also analyzed the effect of plant community composition on belowground biomass and pools.

Both the duration and the magnitude of soil warming influenced the dynamic of total belowground biomass (BPB) and fine-roots and rhizomes separately. The soil warming effect varied along the soil depths. Both changes in carbon and nitrogen concentration in fine-roots and rhizomes and their corresponding biomass contributed to the significant decline in carbon and nitrogen pool in belowground plant biomass along the warming gradient. The change in the functional structure of the plant community was related to the increase in soil temperature. The proportion of forbs increased towards warmer plots and was related to the change in the BPB and soil chemistry. Our findings underline the importance of a functional approach in root research to understand better the key physiological processes like N and C cycling. We highlight the role of soil chemistry and community changes together with warming (duration and magnitude) in the fine-root and rhizome response to climate change. 

How to cite: Bhattarai, B., D. Sigurdsson, B., Sigurdsson, P., Leblans, N., Janssens, I., Truu, J., Truu, M., Kumar Devarajan, A., and Ostonen, I.: Soil warming duration and magnitude affects dynamics of fine-roots and rhizomes and C and N pools in belowground biomass in subarctic grasslands, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12663, https://doi.org/10.5194/egusphere-egu22-12663, 2022.

17:30–17:36
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EGU22-12825
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ECS
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On-site presentation
Jeffrey Beem Miller et al.

Climate and parent material interact to form mineral assemblages that contribute to soil organic matter persistence across a range of time scales. Mineral associated soil organic matter (MAOM, the heavy soil component separated by density fractionation) generally contains more C and persists in soils longer than free or occluded light material. Yet while some MAOM persists for centuries, other forms of MAOM turnover on annual to decadal timescales. In order to predict the response of soil C pools to changes in inputs and decomposition rates under climate change we must be able to distinguish the relatively labile component of this mineral-associated soil C pool from the relatively passive component.

We collected samples in 2001, 2009, and 2019 from 9 sites along a combined gradient of parent material (granite, andesite, basalt) and mean annual temperature (MAT) (6.7°C, 9.1°C, 13.6°C). Mean annual precipitation was similar across all sites (80-130 mm yr-1). We measured the radiocarbon (14C) values of bulk soils, respired CO2, density fractions, and thermal fractions. We used selective dissolution and quantitative x-ray diffraction to determine mineral assemblages. We modeled turnover rates for bulk soil and MAOM using SoilR with C stocks and 14C data as constraints.

Using the difference between respired 14C and bulk 14C as a proxy for soil C protection, we observed a strong negative correlation with poorly crystalline mineral content at all time points, suggesting these secondary minerals play a key role in protecting soil C from decomposition. Poorly crystalline mineral content was greatest in the andesite soils, followed by basalt, then granite soils. Temperature also affected poorly crystalline mineral content, with greater abundances in sites with MAT of 9.1°C than in warmer or colder sites across lithologies.

Mineral assemblages were also related to the change in bulk 14C over time. Between 2001 and 2019, bulk 14C declined 4-5‰ yr-1 faster (p < 0.05) in granite and basalt versus andesite soils at the 9.1°C MAT sites. Within the andesite soils, bulk 14C declined 6‰ yr-1 faster at 13.6°C than 9.1°C (p < 0.05). Overall, slower rates of bulk 14C change were correlated with older mean C ages in the models. When compared within each MAT regime, our models revealed andesite soils to have older mean soil C ages than the basalt or granite soils. Respiration fluxes from these soils were more enriched in 14C than the fluxes from the basaltic or granitic soils, and were also enriched relative to the atmosphere. This indicates active decomposition of older decadally cycling soil C derived from mid-20th century nuclear weapons testing in the andesitic soils but not in the basalt or granite soils.

Measurements of 14C in MAOM and associated thermal fractions (currently underway) will enable us to quantify the relative amounts of MAOM cycling at time scales relevant for improving near-term C budgets not only at our sites, but with implications for improving future models of soil C cycling at broader scales as well. 

How to cite: Beem Miller, J., Rasmussen, C., Hoyt, A., Schrumpf, M., Guggenberger, G., and Trumbore, S.: Temperature and mineralogical effects on decadally cycling mineral associated soil organic matter, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12825, https://doi.org/10.5194/egusphere-egu22-12825, 2022.

17:36–17:42
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EGU22-12918
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ECS
Ezgi Tok and Nazlı Olğun Kıyak

As semi-closed ecosystems, biotic and abiotic properties of cave environments are extensively isolated from the impacts of the surface processes, except for a few environmental parameters. Surface climatic parameters (atmospheric CO2 ratio, temperature, and precipitation amount) and vegetation are known with their impact on the environmental parameters such as the CO2 partial pressure, temperature, and humidity of the cave atmosphere. These properties of cave microclimate are defined over a long-term process of balancing all the input and output heat and mass fluxes under the influence of soil temperature, seepage water content and the chemical/physical properties of sinking streams as well as direct air flux from the outside into the cave. While this interaction between the surface and in-cave environmental parameters exerts a key factor on the hydro/geochemical, and microbiological properties of the cave by altering the biotic and abiotic conditions, cave environments can be considered as long-term archives of the consequences of this interaction by being highly sheltered to the surface processes. This relationship between sediment geochemistry, microbiology and environmental conditions is still not fully understood.

In this study, the relationship between bacterial diversity, sediment geochemistry, and microclimate as three major components of cave ecosystems will be examined in cave environments, the relationship between in-cave and surface atmospheric conditions as well. In order to determine the in-cave environmental conditions, micro-climatic (CO2, temperature, humidity) and environmental (cave water pH, alkalinity) parameters were measured during the fieldwork. Sediment and water (drip water, underground river water and pond water) were sampled in two seasons (summer and winter) aseptically as triplet to determine bacterial community composition of these caves. Water, sediment, and speleothem samples from the caves were examined by Inductively Coupled Plasma - Mass Spectrometry (ICP-MS) and Next Generation Sequencing (NGS) methods to reveal the geochemical and metagenomic features. To observe the changes in cave micro-climate for a year-long period, dataloggers were used.

How to cite: Tok, E. and Olğun Kıyak, N.: Beneath the surface: Climatic, Micro-climatic, Geochemical and Microbiological Approach to Karstic Cave Ecosystem, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12918, https://doi.org/10.5194/egusphere-egu22-12918, 2022.

17:42–17:48
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EGU22-13048
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Highlight
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On-site presentation
Iain Hartley et al.

Physical and chemical stabilisation mechanisms are now known to play critical roles in controlling carbon (C) storage in mineral soils. This has led to suggestions that climate warming-induced C losses may be lower than previously predicted. However, evidence has also been produced that the decomposition of older, and more protected soil organic matter (SOM) is more sensitive to temperature than unprotected and more rapidly decomposing SOM pools. Thus, the extent to which temperature controls C storage in mineral soils remains controversial, and it is not known whether the C stores in soils with large capacities for stabilising C are more, or less, vulnerable to climate warming than the C stored in soils with more limited stabilisation capacities.

By analysing data on >9,000 soil profiles from the World Soil Information Database, we found that, overall, C storage declines strongly with mean annual temperature. However, we observed very large differences in the effect of temperature on C storage in soils with different capacities for stabilising SOM, as indicated by their textural properties. In coarse-textured soils (clay contents less than 20%) with more limited stabilisation capacities, C storage declined strongly with temperature, decreasing by a factor of 1.6 to 2.0 for every 10 oC increase in temperature. However, in fine-textured soils (clay contents greater than 35%) with greater stabilisation capacities, the effect of temperature on C storage was more than three times smaller. This pattern was observed independently in cool and warm regions, and after accounting for potentially confounding factors including plant productivity, precipitation, aridity, cation exchange capacity and pH. The difference in the effects of temperature on C storage in soils with contrasting stabilisation capacities could not, however, be represented by an established Earth system model (ESM). To reduce uncertainties in projections of the effect of climate change on soil C losses, we suggest that ESMs could be evaluated against their ability to simulate the differences in the effects of temperature on C storage in soils with contrasting textural properties.

In conclusion, our results suggest that there are stabilised pools of SOM in fine-textured soils that may be relatively insensitive to the impacts of climate change, but that less protected pools in coarser-textured soils may be substantially more vulnerable to global warming than currently predicted. Finally, given the mismatches between data and model outputs, ESMs may not be predicting accurately the potential magnitude of soil C losses in responses to climate warming or which stocks are most vulnerable.

How to cite: Hartley, I., Hill, T., Chadburn, S., and Hugelius, G.: Temperature effects on carbon storage are controlled by soil stabilisation capacities, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13048, https://doi.org/10.5194/egusphere-egu22-13048, 2022.

17:48–17:54
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EGU22-13184
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ECS
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Virtual presentation
Oliver Donnerhack and Georg Guggenberger

Environmental changes, such as altered precipitation patterns and temperatures, but also the type of
land management, have strong impact on the vegetation structure and the associated soil carbon
storage. Vulnerable ecosystems that have always grown at the limits of system stability have small
resilience and therefore respond to the smallest changes. This is also true for the forest-steppe
ecotones at the southern border of the Mongolian taiga, with their two subtypes of light and dark
taiga. Due to drought stress, this forest only grows on the northern slopes, where the rate
evapotranspiration is smaller. Climatic change, which is very pronounced in these highly continental
areas, leads to water scarcity and thus to higher drought stress as well as an increased risk of forest
fires. In the forest-steppe ecotone in northern Mongolia, light taiga dominated by Betula is increasingly
spreading into areas previously covered by dark taiga representing coniferous forests dominated by
Pinus and Larix. Since soil organic carbon stocks are known to be related to vegetation, in this study
we aimed at assessing the spatial carbon stocks distribution of different forest-steppe ecotones
characterized by different tree compositions by using a multispectral satellite image approach. Based
on Sentinel-2 data, a supervised random forest classification was carried out using the MSAVI index
and carbon stocks from 50 soil profiles of these sites as training data. For the first time, a mean of
multi-year MSAVI was used to compensate the temporal gap between the actual image of vegetation
vitality and the comparatively inert soil organic carbon. The results were validated by ground truthing
on further 36 soil profile measurements. The validation confirmed the accuracy of the classification
and thus led to a valid area calculation. The map based on the measurement results, which was created
by the use of machine learning, illustrates that the significant differences in the spatial distribution of
the taiga subtypes and their soil organic carbon stocks balance each other out in the areas under
consideration. Since the resulting map could be validated by both soil investigations and field survey
experiences, we assume that the applied remote sensing method can be used as a basis for a realistic
area monitoring of the ecosystem under consideration to calculate the spatial change of the carbon
pool. 

How to cite: Donnerhack, O. and Guggenberger, G.: Large scale carbon mapping of forest-steppe ecotones using multispectral satellite data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13184, https://doi.org/10.5194/egusphere-egu22-13184, 2022.

17:54–18:00
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EGU22-13214
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ECS
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On-site presentation
Melanie Brunn et al.

Reduced carbon assimilation by plants and increased net ecosystem exchange are often considered to reduce the overall carbon sink function of drought-stressed ecosystems. However, plants and soil may respond differently under drought, leading to imprecise predictions of carbon sequestration in soil. We determined the net carbon assimilation and related it to soil organic carbon (SOC) stocks as well as to root exudate production to measure belowground carbon investment in mature trees (F. sylvatica and P. abies) exposed to experimental drought for five growing seasons. Despite more than 50 % reduction in net carbon assimilation under drought, SOC stocks increased on average by more than 30 %. The proportion of carbon allocated as root exudates increased two- to threefold under drought. Increasing amounts of carbon in organo-mineral associations suggest increased carbon stability under water-limited P. abies but not under F. sylvatica. Our data indicate that the belowground sink strength increased rapidly for the ecological and economic most relevant tree species in Europe. However, evaluating the ecosystem´s carbon sink strength by using the net ecosystem exchange alone neglects belowground SOC accumulation under drought. Although belowground-invested carbon could contribute to reducing the soil carbon-climate feedback temporarily and may support ecosystem resilience, SOC accumulated primarily in dry mineral topsoil may be vulnerable upon exposure to rewetting events.

How to cite: Brunn, M., Hafner, B., Zwetsloot, M., Sayer, E., Ruehr, N., Weikl, F., Pritsch, K., Hikino, K., Krüger, J., Lang, F., and Bauerle, T.: Experimental drought increased the forest’s belowground sink strength towards temporarily increased topsoil carbon stocks, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13214, https://doi.org/10.5194/egusphere-egu22-13214, 2022.

18:00–18:06
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EGU22-13380
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ECS
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Highlight
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On-site presentation
Sophie F. von Fromm et al.

With climate and land use changes, it is becoming increasingly important to understand not only how much carbon is and will be stored in soils, but also how long this C will remain in soils. Estimates of C age can provide useful information about the timescales on which C will respond to such changes. It is generally accepted that the interaction of climate and soil mineralogy have a strong influence on C age. However, our current understanding is primarily based on findings from temperate regions and from small-scale studies. Large knowledge gaps persist in (sub-)tropical regions where soil processes are often understudied.

Here, we use a systematic continental-scale approach to better understand the processes controlling C age on a larger scale in these understudied soils. In total, 510 samples were analyzed for radiocarbon (Δ14C), consisting of topsoils (0–20 cm) and subsoils (20–50 cm) collected from 30 sites across 14 countries. The sampled soils are part of a comprehensive soil survey (AfSIS) for sub-Saharan Africa, for which soil mineralogy (based on X-ray powder diffraction) and soil chemistry were determined.

Soils with the youngest C ages are generally highly weathered, and are characterized by humid climates, high gross primary productivity (GPP), and a dominance of 1:1 clay minerals. In contrast, older C ages are either found in arid regions characterized by low C inputs and low mineral stabilization, or in seasonal climates, where GPP is high but a portion of the C is stabilized by 2:1 clay minerals and poorly crystalline minerals. Cultivation and erosion appear to play a secondary role at this large scale, but widen the range of C ages.

Our data suggest that soils from seasonal climate zones have the most favorable climatic and pedogenic conditions to stabilize and store C. Yet, they are also the most vulnerable climate zones according to future projections for sub-Saharan Africa. Understanding how the stabilizing minerals will react to climate change is key to understanding short and long-term changes in C storage and stabilization.

How to cite: von Fromm, S. F., Doetterl, S., Butler, B., Trumbore, S., Six, J., Aynekulu, E., Berhe, A. A., Haefele, S., McGrath, S., Shepherd, K., Winowiecki, L., and Hoyt, A.: Soils with seasonal climates have highest potential to stabilize carbon by minerals in sub-Saharan Africa, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13380, https://doi.org/10.5194/egusphere-egu22-13380, 2022.

18:06–18:12
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EGU22-13386
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ECS
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Virtual presentation
Maria Moser et al.

In the global carbon cycle, organic matter in soils represents the major terrestrial pool of carbon, storing roughly twice the amount of carbon as do the atmosphere and vegetation combined. However, under changing environmental conditions, it remains unclear whether soils act as sources or sinks of carbon. Especially soils in alpine ecosystems are subject to undergo changes in their soil organic carbon (SOC) stocks. To disentangle the possible effects of climate change on SOC stocks in alpine environments, the factors which contribute to SOC stabilization have to be known and understood. Recent studies indicated the importance of soil physicochemical parameters governed by weathering of parent material.

To attain a better understanding of how parent material may influence SOC stabilization in alpine ecosystems, five alpine sites in Europe with varying parent material (i.e., Dolomite, Flysch, Gneiss, Greenschist, and Marl) were investigated. Similar climatic conditions, aspect, and slope allowed to analyze the impact of different parent materials on SOC stocks. The geochemical composition of the parent material and the soil, exchangeable cations and effective cation exchange capacity, pH, pedogenic oxides, soil texture, organic carbon and nitrogen contents, and SOC fractions were determined for all soil horizons (i.e., Oh, Ah, Bv, and Cv). The following SOC fractions were physically separated: unprotected, coarse particulate organic carbon (>250 µm), SOC occluded in microaggregates (53 – 250 µm), and SOC in the silt and clay fraction (<53 µm), which is assumed to be predominantly protected via minerals. Linear and non-linear models were computed in order to distill the relative importance of the geochemical parameters on SOC concentrations in the bulk soil (SOCbulk) and the silt and clay fraction (SOCs+c).

Preliminary findings point at the importance of soil depth, texture, and organically complexed oxides as these parameters were found to be among the best predictors for SOCbulk. The concentrations of poorly crystalline aluminum, magnesium, and exchangeable manganese gained importance when predicting SOCs+c. These results align with previous research which has shown the influence of pedogenic oxides on SOC stabilization, Furthermore, the significance of soil depth supports the increasing call of soil scientists to take the entire soil profile into account when analyzing SOC dynamics since large amounts of carbon are stored at depth below the commonly analyzed first 30 cm.

How to cite: Moser, M., Doetterl, S., and Griepentrog, M.: Weathering of soil parent material controls quantity and quality of soil organic carbon in alpine ecosystems, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13386, https://doi.org/10.5194/egusphere-egu22-13386, 2022.